The present invention relates to a method of representing motion of a multiple-articulated object such as a human or an animal, and in particular, to a motion representation method, a motion representing apparatus, a computer graphic apparatus, and a robot controller suitable for facilitating an operation to set and to change a motion of the multiple-hinged object when a size thereof is altered and for enabling various kinds of motions to be represented.
In order to represent in computer graphics such motions as walking and running actions of a human and motions of a horse and a spanworm, a key frame method has been employed in general. According to the key frame method, to generate motions of a multiple-articulated object such as a human or a horse, the user first defines contours thereof at a point of time and at a subsequent point of time, respectively. Contours between these periods are determined based on an interpolation so that the respective contours or shapes thus attained are sequentially displayed in a time-series manner to resultantly produce a motion picture in which the multiple-jointed object seems to make a real action. However, the key frame method is attended with a problem that the contours thus determined in the time-series manner for the motion of the object takes a long period of time, which hence requires a considerably large amount of processing time and which imposes a heavy load on the operator.
Heretofore, to overcome this problem, as described in an article entitled "A Study of Computer Animation Composed of Animation Primitives by Trigonometric Motion Approximation" written in the Proceedings of IECE of Japan, Jan. 1980, Vol. J63-D No. 1, an action of a human is shot by a camera to attain an animation picture thereof on a 16 millimeter (mm) film so as to measure movements of representative points of joints or articulations. For each joint portion above, horizontal and vertical positions X and Y thereof are obtained in centimeters relative to reference positions in a form of a function of time T, thereby determining a locus of the movement of each joint portion. Thereafter, the locus of the movement is approximated by a straight line and a trigonometric curve such that the computer system achieves computations on the approximated curve to attain respective contour data items in a time sequence, which are then sequentially displayed as a motion picture in the graphic system.
According to the prior art above, the movement of each articulation thus obtained through the shooting operation on a 16 mm film is analyzed to extract changes in the X-directional and Y-directional positions relative to the respective reference positions at each point of time, thereby determining the approximated curve of the motion of the human. Consequently, a satisfactory animation picture is developed when the action is to be expressed by the approximated curve. However, the approximated curve cannot be applied to a case, for example, where the size of the object is varied or where dimensional ratios between the respective joints are altered in the motion. In this case, there arises a problem that the shooting operation is required to be again actually achieved on the object with the pertinent size and/or with the associated ratio between the joints, which leads to a limited degree of freedom for representing the animation. That is, according to the conventional technology, when generating a motion picture of a multiple-jointed object in the computer graphic system, the image can be presented only as an analogy of the real object having thus undergone the shooting operation. This means that various actions cannot be developed in computer graphics. For example, only an ordinary walking action of a human shot by the camera can be displayed in the graphic image. Namely, even when the ordinary or standard action is modified, a motion picture of, for example, a violent walking action or a joyful or pleasant walking motion cannot be obtained. Consequently, heretofore, to express such an action above, for example, a human model is required to actually walk with a violent feeling to be shot by a camera so as to attain an image of the violent walk, which is then analyzed to implement an objective animation picture. In other words, for example, when producing a motion picture of animals, insects, and imaginary objects of which various actions cannot be actually shot by a camera, various movements thereof cannot be easily presented in computer graphics.
In addition, it has been impossible in the conventional technology to produce an action with a human or emotional feature, which is usually expressed, for example, by a feature. That is, a characteristic action with a human emotion cannot be reflected on animation picture of the multiple-jointed object.